1. Field of the Invention
The invention relates to a method for fabricating a liquid crystal display and more particularly to a method for fabricating a pixel structure of liquid crystal display.
2. Description of the Related Art
Thin film transistors (TFT) drive pixels in active matrix liquid crystal displays, active matrix organic light-emitting displays, image sensors and the like. Generally, TFT used in these apparatuses are formed of silicon semiconductor thin film.
Large area electronic devices (e.g., LCD (liquid crystal display)) typically include large arrays of thin-film transistors (TFTs) for addressing individual elements of the electronic device (e.g., pixels of the displays). As the demand for larger electronic devices, such as LCD displays, continues to rise, the TFT arrays used in these devices must include increasing numbers of TFTs and more complex interconnect structures. In addition, the need for large display devices complicates the fabrication of these devices using conventional semiconductor processes. In combination, these factors result in ever-increasing TFT array size and complexity.
To reduce some of the costs associated with the production of these larger LCD displays, a lift-off process is sometimes used to generate patterned structures that device openings (vias) and gaps between the various structures that make up the TFT array. In a conventional lift-off process, a base layer on which a patterned photoresist layer is formed is blanket-coated with an overlying thin film, typically a metal layer. Then, the patterned photoresist layer is stripped, which removes those portions of the metal layer formed on top of the patterned photoresist layer, leaving a patterned metal layer on the base layer. By eliminating the need for a separate etch process to create the patterned metal layer, the conventional (photoresist-based) lift-off process can simplify the overall production process, thereby reducing production costs. However, patterning the photoresist layer still requires a photolithography process. For cost-reduction purposes, it is generally desirable to minimize the number of photolithography process steps required. This is not only due to the demanding nature of the photolithography process itself, but also due to the time and costs involved in producing the delicate photomasks used in the photolithography process.
Accordingly, what is needed is a method for forming patterned structures for large area electronic devices that does not require the need for photolithographic masks (self-aligned) to save time and reduce fabrication cost. An exposure process technique so-called “back exposure” has been proposed to form desired transparent, colored and fine patterns on a transparent substrate by exposure to light from the back of the substrate with an opaque pattern as photo-mask.
The back exposure, however, needs numerous and complicated preparations. Further, there is no reference that discloses a method to form a passivation layer by back exposure. Therefore, it is necessary to develop a novel method for forming a passivation layer of LCDs by back exposure without increasing process complexity.